fix: QA issues — composite index, anchors, fallbacks

- Add composite index ix_translation_records_run_source_hash
  for NOT EXISTS dedup subquery performance + Alembic migration
- Remove duplicate #endregion in orchestrator.py (INV_3)
- Replace hardcoded RU fallback 'Статус' with 'Status'
- Add early return guard to loadMoreRecords()
- Show records summary always when recordsTotal > 0

frontend/src/lib/components/translate/TranslationRunResult.svelte

@@ -168,6 +168,7 @@ import { SvelteSet } from "svelte/reactivity";
 
 	/** Load next page of unique rows and append to records list. */
 	async function loadMoreRecords() {
+		if (recordsLoadingMore) return;
 		recordsLoadingMore = true;
 		const nextPage = recordsPage + 1;
 		try {
@@ -319,7 +320,7 @@ import { SvelteSet } from "svelte/reactivity";
 						</button>
 					</div>
 					<div>
-						<span class="text-text-muted">{_t.translate?.run?.status_label || 'Статус'}</span>
+						<span class="text-text-muted">{_t.translate?.run?.status_label || 'Status'}</span>
 						<span class="ml-1 text-xs font-medium text-text">{getRunStatusLabel(status.status)}</span>
 					</div>
 					<div>
@@ -586,7 +587,7 @@ import { SvelteSet } from "svelte/reactivity";
 								</tbody>
 							</table>
 						</div>
-						{#if !allRecordsLoaded && recordsTotal > records.length}
+						{#if recordsTotal > 0}
 							<p class="text-xs text-text-subtle mt-1">
 								{(_t.translate?.run?.showing_records || 'Showing {count} of {total} unique rows.')
 									.replace('{count}', records.length)